Generally, there is known a shaft seal device to be fixed to a container that separates a high-pressure fluid and a low-pressure fluid from each other and sealing a shaft-penetrating portion of the container through which a rotational shaft extends. For example, a rotational shaft, which rotates the impeller of a vertical pump, extends through a pump casing, and a shaft-penetrating portion, through which the rotational shaft extends, is sealed by a shaft seal device so as to prevent a liquid from leaking out of the shaft-penetrating portion. In terms of the vertical pump, the container is the pump casing, the high-pressure fluid is a liquid flowing within the pump casing, and the low-pressure fluid is atmosphere outside of the pump casing. Such a shaft seal device typically incorporates a seal mechanism such as a gland packing seal, a mechanical seal, or a floating seal.
A gland packing seal is brought into contact with an outer circumferential surface of a rotational shaft to prevent a liquid leakage by contact pressure between them. A mechanical seal has a rotating ring rotatable together with a rotational shaft and a stationary ring fixed to a stationary member, such as a housing. The rotating ring and the stationary ring are kept in contact with each other, preventing a liquid leakage. A floating seal has a sleeve fixed to an outer circumferential surface of a rotational shaft, and a seal ring facing the sleeve. An extremely small gap is formed between the seal ring and the sleeve, allowing only a minute amount of liquid to leak therethrough.